Microbial Shifts in Metisa plana (Lepidoptera: Psychidae) Larvae Exposed to Bacillus thuringiensis and Flubendiamide

Microbial communities in the insect body, especially in the gut, are crucial for host development, health, and environmental adaptation. However, little is currently understood about how these communities react to anthropogenic stressors, particularly when pesticides are used. This study aims to investigate the independent and synergistic effects of the biopesticide, Bacillus thuringiensis MPOB Bt1 (MPOB Bt1) and the synthetic diamide insecticide, flubendiamide (Fbd) on the microbial community of the oil palm bagworm, Metisa plana larvae. Larvae were collected at zero (DAT0), one (DAT1), and three days (DAT3) post-treatment and analyzed for bacterial genus abundance and network responses using shotgun metagenomic-derived taxonomic profiling. Analysis of larval microbial community shifts showed that the combined MPOB Bt1-Fbd treatment resulted in a significant increase in microbial richness, with network density rising from 0.1354 at DAT0 to 0.2279 at DAT3 compared to the individual Fbd treatment. Pearson correlation analysis also showed that the combined MPOB Bt1-Fbd treatment was associated with the growth of the microbiome members that can co-occur with Bacillus . The positive co-occurrence patterns between Bacillus and the genera Enterobacter and Pseudomonas in the combined MPOB Bt1-Fbd treatment may reflect treatment-associated microbial shifts during dysbiosis, with their ecological and functional relevance requiring further investigation. This preliminary study provides insights into microbial community responses to the mixture of MPOB Bt1-Fbd compared to the individual treatments. Further functional analysis of the microbial community is needed to clarify the potential roles of these taxa in pathogenicity, treatment response, and pesticide tolerance in the development of M. plana control methods in the future.